Adjustable fume tube burner

ABSTRACT

A method of forming an optical fiber preform includes the steps: igniting a burner having a fume tube assembly to produce a first spray size of silicon dioxide particles; depositing the silicon dioxide particles on a core cane to produce a soot blank; and adjusting an effective diameter of an aperture of the fume tube assembly to produce a second spray size of the silicon dioxide particles. The second spray size is larger than the first spray size.

This application claims the benefit of priority under 35 U.S.C. § 119 ofU.S. Provisional Application Ser. No. 62/472,164 filed on Mar. 16, 2017the content of which is relied upon and incorporated herein by referencein its entirety.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to burners, and moreparticularly to adjustable fume tubes of silica particle burners.

BACKGROUND

Outside vapor deposition (OVD) processes are used for the production ofoptical fiber preforms. Certain burners may be able to make one preformblank in a single run. Both soot capture efficiency and laydown rate areimportant to the overall cost of fiber manufacturing. However, increasedlaydown rates often have a deleterious effect on the efficiency of thesoot capture by the optical fiber preform. Accordingly, new methods andsystems of increasing soot capture efficiency and laydown rate may bedesirable.

SUMMARY OF THE DISCLOSURE

According to at least one example of the present disclosure, a method offorming an optical fiber preform includes the steps: igniting a burnerhaving a fume tube assembly to produce a first spray size of silicondioxide particles; depositing the silicon dioxide particles on a corecane to produce a soot blank; and adjusting an effective diameter of anaperture of the fume tube assembly to produce a second spray size of thesilicon dioxide particles. The second spray size is larger than thefirst spray size.

According to another example of the present disclosure, a burnerincludes a back block and a face block. The face block defines aplurality of gas emitting regions. A fume tube assembly extends throughthe face block and is surrounded by the gas emitting regions. The fumetube assembly includes a first fume tube coupled to the face block. Asecond fume tube is positioned within the first tube. An aperture isdefined at an end of the fume tube assembly. An actuator is coupled withthe second fume tube and configured to move the second fume tube withinthe first fume tube to adjust an effective diameter of the aperture.

According to another example of the present disclosure, a burnerincludes a face block defining a plurality of gas emitting regions. Afume tube assembly extends through the face block and is surrounded bythe gas emitting regions. The fume tube assembly includes a first fumetube. A second fume tube is movably positioned within the first tube anddefines an exterior surface. The exterior surface is tapered. Anaperture is defined at an end of the fume tube assembly. An actuator iscoupled with the second fume tube and configured to move the second fumetube within the first fume tube to variably adjust an effective diameterof the aperture.

These and other features, advantages, and objects of the presentdisclosure will be further understood and appreciated by those skilledin the art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of the figures in the accompanyingdrawings. The figures are not necessarily to scale, and certain featuresand certain views of the figures may be shown exaggerated in scale or inschematic in the interest of clarity and conciseness.

FIG. 1 is a cross-sectional view of a burner, according to at least oneexample;

FIG. 2A is a perspective view of a fume tube assembly removed from aburner, according to at least one example;

FIG. 2B is a perspective view of the fume tube assembly of FIG. 2A in adifferent state;

FIG. 3 is a perspective view of a fume tube assembly removed from theburner, according to at least one example;

FIG. 4A is an enhanced view of section IVA of FIG. 1, according to atleast one example;

FIG. 4B is an enhanced view of section IVB of FIG. 1, according to atleast one example;

FIG. 4C is an enhanced view of section IVC of FIG. 1, according to atleast one example;

and

FIG. 5 is a flow diagram of operating the burner, according to at leastone example.

DETAILED DESCRIPTION

Additional features and advantages of the invention will be set forth inthe detailed description which follows and will be apparent to thoseskilled in the art from the description, or recognized by practicing theinvention as described in the following description, together with theclaims and appended drawings.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itself,or any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

In this document, relational terms, such as first and second, top andbottom, and the like, are used solely to distinguish one entity oraction from another entity or action, without necessarily requiring orimplying any actual such relationship or order between such entities oractions.

Referring now to FIGS. 1-5, reference numeral 10 generally designates aburner. The burner 10 includes a back block 14 and a face block 18. Theface block 18 defines a plurality of gas emitting regions 22. A fumetube assembly 26 extends through the face block 18 and is surrounded bythe gas emitting regions 22. The fume tube assembly 26 includes a firstfume tube 30 coupled to the face block 18. A second fume tube 34 ispositioned within the first fume tube 30. An aperture 38 is defined atan end of the fume tube assembly 26. An actuator 42 is coupled with thesecond fume tube 34 and configured to move the second fume tube 34within the first fume tube 32 to adjust an effective diameter of theaperture 38.

Referring now to FIG. 1, the burner 10 may be used in the formation ofcore soot preforms, optical fiber preforms 50 and/or for the productionof silicon dioxide, or silica, particles (e.g., soot). Further, theburner 10 may be used to provide an overclad layer to a core. The silicasoot produced by the burner 10 may include one or more dopants such asGeO₂, TiO₂, B₂O₃, Al₂O₃, P₂O₅ and the like. In core soot preformexamples, soot produced by the burner 10 may be applied to a bait rod toform a core soot blank around the bait rod. In optical fiber preform 50examples, the preform 50 includes a core cane 54 and a soot blank 58.The core cane 54 may be composed of a consolidated glass (e.g., agermanium doped core soot preform consolidated into void-free glass)and/or other transparent materials. The soot blank 58 is positioned andsurrounds the core cane 54. The soot blank 58 is composed of silica sootwhich is produced by the burner 10. According to various examples, thesoot blank 58 may be a plurality of silica particles. The soot blank 58may include one or more dopants for affecting the optical properties ofoptical fibers produced from the optical fiber preform 50. The silicasoot may be applied to the core cane 54 and the soot blank 58 from theburner 10 via outside vapor deposition which may otherwise be referredto herein as spraying or a laydown process. The optical fiber preform 50may be rotated while the silica soot from the burner 10 is sprayed ontothe core cane 54 and/or soot blank 58. The optical fiber preform 50 maybe consolidated once the soot blank 58 has reached a predetermined sizeand an optical fiber drawn therefrom.

The soot blank 58 of the optical fiber preform 50 grows (e.g., inthickness and diameter) with time as silica soot from the burner 10 isdeposited thereon. In other words, the target (e.g., the soot blank 58)of the burner 10 grows in size with time. For example, the optical fiberpreform 50 may grow from about 20 mm in diameter (e.g., essentially thediameter of the core cane 54) to about 300 mm in size (e.g., thediameter of the core cane 54 and soot blank 58) over the course of thedeposition or laydown process. As such, deposition of the silica sootonto the optical fiber preform 50 may be broken into a plurality ofstages. According to at least one example, the deposition of the silicasoot from the burner 10 onto the optical fiber preform 50 may be brokeninto an early-stage, a transition stage, and a late stage.

In the early stage, the optical fiber preform 50 may provide a smalltarget area (e.g., just the core cane 54) for the burner 10 and as sucha first spray size of the silica soot particles from the burner 10 maybe small. The first spray size may have a diameter of from about 0.5 cmto about 2.4 cm, or from about 0.8 cm to about 2.0 cm at from about 8 cmto about 10 cm from the aperture 38 of the fume tube assembly 26. In aspecific example, the first spray size may have a diameter of about 1.2cm at about 9 cm from the aperture. The spray size of the burner 10 mayremain constant at the first spray size during the early stage. Keepingthe first spray size of the burner 10 small while the optical fiberpreform 50 is small in the early stage may be advantageous in increasingthe soot capture, or efficiency, of the burner 10. For example, asmaller spray size may ensure that a greater quantity of the silica sootis captured by the preform 50 and does not merely pass by the preform50. The early-stage of the laydown process may encompass the first 40minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100minutes, 110 minutes, 120 minutes or 130 minutes of the depositionprocess. It will be understood that the size of the optical fiberpreform 50 at the end of the early-stage may vary from process toprocess and may be dependent on factors such as size of the burner 10,desired size of the soot blank 58 and/or overall size of the opticalpreform 50.

As the optical fiber preform 50 grows in size, the laydown process maychange to the transition state. In the transition state, the effectivediameter of the aperture 38 of the fume tube assembly 26 may be adjustedand/or increased as explained in greater detail below. The increasedeffective diameter of the aperture 38 may provide a second spray size ofthe silica soot particles toward the optical fiber preform 50. Accordingto various examples, the second spray size may be larger (e.g., wider,taller, and/or thicker) than the first spray size. For example, thesecond spray size may have a diameter of from about 1.0 cm to about 3.0cm, or from about 1.2 cm to about 1.8 cm at from about 8 cm to about 10cm from the aperture 38 of the fume tube assembly 26. In a specificexample, the second spray size may have a diameter of about 1.5 cm atabout 9 cm from the aperture. Although described as a stage, it will beunderstood that the transitional stage and the adjusting of theeffective diameter of the aperture 38 may take place instantaneously orgradually over a period of time (e.g., greater than or equal to aboutone second, one minute, or greater than or equal to about 10 minutes).

The late stage state of the deposition process may take place once theoptical fiber preform 50 reaches a predetermined thickness or depositiontime. The late stage state of the deposition process may begin at about40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes,100 minutes, 110 minutes, 120 minutes, 130 minutes into the laydownprocess and extend to the end of the process run. The spray size of theburner 10 may remain constant at the second spray size during the latestage. During the late stage state of the laydown process, the secondspray size, which is larger than the first spray size, may facilitate ahigher deposition rate of the silica soot onto the soot blank 58 whilemaintaining a desired level of silica soot capture (e.g., a desiredlevel of efficiency). In other words, as the thickness of the soot blank58 increases, it is able to accommodate the larger second spray size. Assuch, the silica soot from the burner 10 may be applied with a higherdeposition rate. The amount of gas emitted from the gas emitting regions22 of the burner 10, as well as the amount of silica soot produced bythe fume tube assembly 26, may be increased in the late stage.

It will be understood that other examples of the laydown process may beimplemented. For example, the laydown process may be divided into lessthan or greater than three stages. For example, when the fume tubeassembly 26 includes greater than two fume tubes, the laydown processmay include an additional transition stage and an intermediate stagebetween the transition stages. In examples of the burner 10 where theeffective diameter of the aperture 38 may be smoothly transitioned overa majority or the entirety of the laydown process, the laydown processmay effectively be a single transition stage, or the transition stagemay extend over a large portion (e.g., greater than or equal to about 30min) of the laydown process with an early stage and a late stage oneither side of the transition stage.

Division of the deposition process into the early-stage, transitionstage and late stage, and the adjusting of the effective diameter of theaperture 38 may not only be advantageous in increasing the captureefficiency of the silica soot by the optical fiber preform 50, but mayalso be advantageous in increasing the rate at which the silica sootparticles are adhered to the optical fiber preform 50 (e.g., therebyshortening manufacturing time).

Still referring to FIG. 1, the burner 10 may be positioned within one ormore housings which aid in generally directing the silica soot towardthe optical fiber preform 50. The burner 10 has five main components:the face block 18, a manifold plate 70, the back block 14, the fume tubeassembly 26, and a burner mounting block 74. The face block 18, themanifold plate 70, the back block 14, the fume tube assembly 26, and theburner mounting block 74 may be composed of a metal, a polymer, aceramic or combinations thereof. Examples of suitable metals may includealuminum, stainless steel and other metals which can be readilymachined. It will be understood that the face block 18, the manifoldplate 70, the back block 14, the fume tube assembly 26, and the burnermounting block 74 may each be made of the same material or a differentmaterial.

In use, the face block 18, manifold plate 70, back block 14 and fumetube assembly 26 are assembled as described below to form a subassemblywhich is mounted to the burner mounting block 74 through bolts 78. Theactuator 42 is positioned rearward of the burner 10, and coupled to thesecond fume tube 34. It will be understood that the actuator 42 may becoupled to the burner mounting block 74 without departing from thedisclosure provided herein. The actuator 42 is configured to move thesecond fume tube 34 coaxially within the first fume tube 30.Additionally or alternatively, the actuator 42 may be coupled with thefirst fume tube 30 such that the first fume tube 30 may move relative tothe second fume tube 34. Further, the actuator 42 may be configured tofunction as a gas supply to the first and/or second fume tubes 30, 34 asexplained in greater detail below. The fume tube assembly 26 may bepress fit into back block 14. In this way, a precision alignment isachieved between the fume tube assembly 26 and the back block 14. Theface block 18 of the burner 10 has a sliding fit over fume tube assembly26 which provides alignment, as well as easy disassembly, of thesecomponents. In other words, the fume tube assembly 26 is extendingthrough the face block 18.

During operation, the burner 10 is configured to emit a plurality ofgasses. Some of the gasses may be shield gasses while other gasses areburned to aid in the production of the silica soot. The gas pumpedthrough the first and/or second fume tubes 30, 34 of the fume tubeassembly 26 is a fumed, or vaporized, silicon tetrachloride (Siltet)and/or octamethylcyclotetrasiloxane (OMCTS) and O₂ mixture. Althoughdisclosed in connection with Siltet and OMCTS, it will be understoodthat the any silica producing compound may be provided through the fumetube assembly 26. For example, tetraorthosilicate (TEOS) may also beprovided through the fume tube assembly 26. As explained above, theactuator 42 may be the source of the Siltet and/or OMCTS and/or the O₂.In the depicted example, the Siltet and/or OMCTS and O₂ enter the burner10 through the fume tube assembly 26, and ultimately exits the fume tubeassembly 26 through the aperture 38. It will be understood that the fumetube assembly 26 may also include one or more inert gasses (e.g., N₂) inaddition to the Siltet and/or OMCTS and O₂ without departing from theteachings provided herein. The burner 10 may have a flow rate of Siltetand/or OMCTS of from about 6 grams per minute to about 25 grams perminute, or from about 10 grams per minute to about 15 grams per minute.In a specific example, the flow rate of Siltet and/or OMCTS may be about12.5 grams per minute. The flow rate of the O₂ through the fume tubeassembly 26 may be from about 1 slpm to about 10 slpm, or from about 2.5slpm to about 8 slpm. In a specific example, the flow rate of O₂ throughthe fume tube assembly 26 may be about 5.5 slpm.

Gas receiving apertures 90 of the back block 74 mate with gas supplylines and gas tight fittings to receive a CH₄ and O₂ premix. The CH₄ andO₂ premix enters the burner mounting block 74, proceeds through a gaspassage 130 in the back block 14, passes through pressure equalizingorifices of manifold plate 70, and ultimately exits the burner's facethrough a gas burner region 134. The burner 10 may have a flow rate ofCH₄ of from about 1 slpm to about 7 slpm, or from about 2 slpm to about5 slpm. In a specific example, the flow rate of CH₄ may be about 3.5slpm. The burner 10 may have a flow rate of premix O₂ of from about 1slpm to about 7 slpm, or from about 2 slpm to about 5 slpm. In aspecific example, the flow rate of O₂ may be about 2.8 slpm. The CH₄ andO₂ premix may be ignited and burned to provide heat which combusts theOMCTS and O₂ mixture to produce the silica soot. The combustion of theOMCTS and O₂, along with the shield gasses, propels the silica soottoward the optical fiber preform 50.

Inert gas receiving apertures receive an innershield N₂. The innershieldN₂ enters burner mounting block 74 through a gas receiving aperture,proceeds through a gas passage in the back block 74, enters a centralaperture 110, passes through an integral inner shield manifold of themanifold plate 70, and ultimately exits a face of the burner 10 throughinner shield region 114. The burner 10 may have an innershield N₂ flowrate of from about 1 slpm to about 7 slpm, or from about 2 slpm to about5 slpm. In a specific example, the burner 10 may have an innershield N₂flow rate of about 3.2 slpm.

Outershield O₂ enters the burner mounting block 74, proceeds through agas passage and into an inner annulus 118, passes through a pressureequalizing orifice of the manifold plate 70, and ultimately exits a faceof the burner 10 through outershield regions 122 and 126. The burner 10may have an outer shield O₂ flow rate of from about 4 slpm to about 20slpm, or from about 6 slpm to about 13 slpm. In a specific example, theouter shield O₂ flow rate may be about 9.9 slpm. As such, theoutershield regions 122 and 126, inner shield region 114 and the gasburner region 134 may correspond to the gas emitting regions 22.

Referring now to the example depicted in FIGS. 2A and 2B, the fume tubeassembly 26 includes both the first fume tube 30 and the second fumetube 34. The first fume tube 30 defines a first exterior surface 30A anda first interior surface 30B. The second fume tube 34 defines a secondexterior surface 34A and a second interior surface 34B. The secondexterior surface 34A of the second fume tube 34 is slidably coupled tothe first interior surface 30B of the first fume tube 30. It will beunderstood that the slidably coupled interface between the secondexterior surface 34A and the first interior surface 30B may allow thefirst and second fume tubes 30, 34 to coaxially move relative to oneanother. For example, as explained above, the actuator 42 (FIG. 1) maybe configured to move the first and/or second fume tubes 30, 34 relativeto one another. For ease of explanation, the second fume tube 34 may bedescribed as the movable component, or movable relative to the firstfume tube 30, but it will be understood that the first and/or secondfume tubes 30, 34 may be moved relative to one another without departingfrom the disclosure provided herein.

The first and second fume tubes 30, 34 may be made from a metal, aceramic and/or combinations thereof. In metal examples, the metal may bea stainless steel (e.g., 303 stainless steel) and/or tungsten carbide(e.g., a composite material composed of tungsten carbide ceramicsdisposed within a cobalt matrix). Examples where the first and secondfume tubes 30, 34 are composed of a hard metal and/or ceramic may beadvantageous not only in providing scratch resistance, but also inallowing the precise formation of the first and second fume tubes 30,34.

An inside diameter of the first fume tube 30 may be from about 1 mm(0.04 inches) to about 4 mm (0.16 inches), or from about 2 mm (0.08inches) to about 3 mm (0.12 inches). An inside diameter of the secondfume tube 34 may be from about 0.5 mm (0.02 inches) to about 5.5 mm(0.22 inches), or from about 2.0 mm (0.06 inches) to about 2.8 mm (0.11inches). It will be understood that the inside diameter of the first andsecond fume tubes 30, 34 may take any of the values between thedisclosed ranges. According to various examples, the outer diameter(e.g., the second exterior surface 34A) of the second fume tube 34 maybe substantially, or approximately, equal to, that of the insidediameter (e.g., the first interior surface 30B) of the first fume tube30 such that no gap exists between the first and second fume tubes 30,34. It will be understood that a gap may be defined between the firstand second fume tubes 30, 34 without departing from the teachingsprovided herein.

The aperture 38 is defined at an end of the fume tube assembly 26 andhas an effective diameter. The effective diameter of the aperture 38 isthe diameter of the fume tube assembly 26 through which the Siltetand/or OMCTS and O₂ may exit. The effective diameter of the aperture 38may correspond to an inner diameter of one of the fume tubes of the fumetube assembly 26 in some examples (e.g., FIGS. 2A-3), or may correspondto an intermediate value between the inner diameters of the fume tubesof the fume tube assembly 26 (e.g., FIGS. 4A-4C). As will be explainedin greater detail below, the effective diameter of the aperture 38 maybe adjusted to allow for a change in the spray size of silica sootparticles which are produced by the burner 10. For example, a smallereffective diameter may produce the relatively smaller first spray sizeand a larger effective diameter may produce the relatively larger secondspray size. The effective diameter of the aperture 38 may be governed bythe positioning of the first and second fume tubes 30, 34. For example,the effective diameter of the aperture 38 may become the inside diameterof the first or second fume tubes 30, 34 depending on the relativepositioning of the first and second fume tubes 30, 34. Accordingly,using the actuator 42 to move the first and/or second fume tubes 30, 34relative to one another adjusts the effective diameter of the aperture38. In a first example, the aperture 38 may have an effective diametersubstantially equal to the inside diameter of the second fume tube 34when the ends of the first and second fume tubes 30, 34 aresubstantially flush with one another. In a second example, the aperture38 may have an effective diameter substantially equal to the insidediameter of the first fume tube 30 when an end of the second fume tube34 is retracted into the first fume tube 30, or position rearwardly ofan end of the first fume tube 30. The end of the second fume tube 34 maybe positioned rearwardly of the end of the first fume tube 30 by fromabout 2.0 mm to about 10.0 mm or from about 4 mm to about 6 mm inwardfrom the aperture 38. In other words, the fume tube assembly 26 may havea stepped appearance when the second fume tube 34 is retracted into thefirst fume tube 30.

Positioning of the first and second fume tubes 30, 34 to adjust theeffective diameter of the aperture 38 may be advantageous in adjustingthe spray size of the burner 10 based on the stage at which the silicasoot laydown process is at. For example, during the early stage, whenthe relatively smaller first spray size is desirable, the ends of thefirst and second fume tubes 30, 34 may be substantially flush with oneanother such that the effective diameter of the aperture 38 is narrow(e.g., the diameter of the second fume tube 34). During the transitionalstage, the actuator 42 may move the first and/or second fume tubes 30,34 such that the effective diameter of the aperture 38 is substantiallythat of the inside diameter of the first tube 30. As such, the effectivediameter of the aperture 38 is increased to produce the relativelylarger second spray size which may be desirable for the late stage ofthe laydown process.

Referring now to FIG. 3, the depicted example of the fume tube assembly26 includes a third fume tube 140. The third fume tube 140 may define athird exterior surface 140A and a third interior surface 140B. The thirdexterior surface 140A may be slidably coupled with the second interiorsurface 34B of the second fume tube 34. The third fume tube 140 may becomposed of substantially the same materials as the first and secondfume tubes 30, 34 or may be composed of a different material. An insidediameter of the third fume tube 140 may be from about 0.1 mm to about 4mm, or may be from about 0.5 mm to about 3 mm.

Similarly to the example depicted in FIGS. 2A and 2B, the third tube 140may be coupled to the actuator 42 (FIG. 1) and configured to movecoaxially with the first and second fume tubes 30, 34. Movement of thethird fume tube 140 may change the effective diameter of the aperture 38in a substantially similar manner to that described in connection withthe example of FIGS. 2A and 2B. For example, when the ends of the first,second and third fume tubes 30, 34, 140 are substantially flush with oneanother, the effective diameter of the aperture 38 may be substantiallyequal to that of the inside diameter of the third fume tube 140. As thefirst, second and/or third fume tubes 30, 34, 140 move coaxiallyrelative to one another, the effective diameter of the aperture 38 maybe changed (e.g., increase and/or decrease).

Use of the third fume tube 140 may be advantageous in increasing theefficiency of the silica set laydown process as compared to use of onlythe first and second fume tubes 30, 34. For example, use of the thirdfume tube 140 may allow the silica set laydown process to be broken intoa greater number of stages (e.g., an additional laydown stage and anadditional transitional stage) which may increase the capture efficiencyof the silica set laydown process. For example, in the early stage thefirst, second and third fume tubes 30, 34, 140 may be substantiallyflush with one another such that the effective diameter the aperture 38is that of the third fume tube 140 and thereby produces the relativelysmaller first spray size. A transitional stage may exist where the thirdfume tube 140 is retracted into the fume tube assembly 26 to create astepped region similar to that described above in connection with thefirst and second fume tubes 30, 34. This may allow an intermediatelaydown stage where the effective diameter of the aperture 38 issubstantially equal to that of the second fume tube 34 which may providean intermediate spray size. Next, a second transition stage may occurwhere the second fume tube 34 is retracted into the first fume tube 30such that the effective diameter of the aperture 38 is changed to thatof the inside diameter of the first fume tube 30 thereby producing therelatively larger second spray size. With the increased number of spraysizes afforded by the third fume tube 140, the resulting spray size ofthe burner 10 may be more accurately tailored to the size of the opticalfiber preform 50 which may increase the capture rate, or efficiency, ofthe burner 10.

Referring now to the depicted example of FIGS. 4A-C, the second tube 34is coaxially positioned within the first tube 30 to define a gap 148. Inother words, the exterior surface 34A of the second tube 34 may have asmaller outside diameter than the inside diameter of the first tube 30.Similar to other examples, the first and second fume tubes 30, 34 arecoaxially movable relative to one another. For example, the actuator 42may be configured to move the first and second fume tubes 30, 34coaxially relative to the first fume tube 30. It will be understood thatthe actuator 42 (FIG. 1) may further be configured to move the first andsecond fume tubes 30, 34 in a translational manner in such an example.As will be explained in greater detail below, movement of the first andsecond fume tubes 30, 34 relative to one another may adjust theeffective diameter of the aperture 38 by decoupling the first and secondfume tubes 30, 34 from one another.

In the depicted example, the first fume tube 30 defines a first taperedregion 30C and the second fume tube 34 defines a second tapered region34C. The first tapered region 30C may be tapered in a radially inwarddirection toward a center axis of the first fume tube 30 such that aninner diameter of the first tube 30 is smaller proximate the aperture 38relative to an inner diameter over the rest of the first tube 30. Thefirst tapered region 30C may be tapered at an angle β. The angle β maybe less than or equal to about 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2° orless than or equal to about 1°. The second tapered region 34C may betapered in a radially inward direction, similar to that of the firsttapered region 30C, such that an outer diameter of the second fume tube34 is smaller proximate the aperture 38 than an outside diameter of therest of the second fume tube 34. The second tapered region 34C may betapered at an angle α. The angle α may be less than or equal to about10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, or less than or equal to about 1°.According to various examples, the angles α and β may be complementaryto one another such that the first tapered region 30C flushly engages,or couples, the second tapered region 34C of the second fume tube 34.

Similarly to the depicted examples of FIGS. 2A, 2B and 3, the aperture38 is defined proximate the end of the fume tube assembly 26. In thedepicted example of FIGS. 4A-C, however, the aperture 38 may extendbeyond the end of the first fume tube 30. In other words, where thesecond tapered region 34C of the second fume tube 34 extends beyond theend of the first fume tube 30, the aperture 38 may be solely defined bythe second fume tube 34 (e.g., the effective diameter of the aperture 38would be the inside diameter of the second fume tube 34). In thedepicted example, the Siltet and/or OMCTS and O₂ travel through both thesecond tube 34 as well as within the gap 148 defined within the firsttube 30. By decoupling the second tapered region 34C from the firsttapered region 30C the gap 148 may extend between the first and secondtapered regions 30C, 34C and allow the Siltet and/or OMCTS and O₂present within the gap 148 to exit the fume tube assembly 26 proximatethe aperture 38. Further retraction of the second fume tube 34 into thefirst fume tube 30 may increase the size of the gap 148 between thefirst and second tapered regions 30C, 34C, which may allow an increasedamount of Siltet and/or OMCTS and O₂ to escape proximate the aperture38. Accordingly, moving the first and second fume tubes 30, 34 relativeto one another may adjust the amount of Siltet and/or OMCTS and O₂ whichis allowed to exit, thereby variably adjusting the effective diameter ofthe aperture 38.

In an exemplary operation (e.g., soot laydown process) of the presentlydepicted fume tube assembly 26, the fume tube assembly 26 may begin(e.g., an early stage of the laydown process) in the configurationdepicted in FIG. 4A. In the depicted stage, the first and second taperedregions 30C, 34C are coupled to one another, and the second tube 34extends beyond the first tube 30. In such a configuration, the effectivediameter of the aperture 38 is that of the inside diameter of the secondtube 34. As the inside diameter of the second fume tube 34 is smallerthan the inside diameter of the first tube 30 at the first taperedregion 30C, the depicted configuration may offer the relatively smallerfirst spray size. Using the actuator 42, the first and/or second fumetubes 30, 34 may be moved (e.g., coaxially) relative to one another suchthat the end of the second fume tube 34 is positioned flush with the endof the first fume tube 30 (e.g., as shown in FIG. 4B). As the secondfume tube 34 is retracted into the first fume tube 30, the first andsecond tapered regions 30C, 34C decouple and allow gas (e.g., OMCTS andO₂) present in the fume tube assembly 26 to begin passing through thegap 148 between the first and second tapered regions 30C, 34C. Gassesexiting the gap 148 and passing by the first and second tapered regions30C, 34C may cling, or follow, the exterior surface of the secondtapered region 34C which results in a larger effective diameter of theaperture 38. Such a clinging of the gas to the second tapered region 34Cmay be known as a “wall effect.” As the second fume tube 34 is retractedto the configuration depicted in FIG. 4B, the effective diameter of theaperture 38 is proportionally increased as more gas exits the gap 148,and less gas clings to the exterior surface of the second tapered region34C. As the second fume tube 34 continues to be retracted into the firstfume tube 30 to ultimately reach the configuration depicted in FIG. 4C,the effective diameter of the aperture 38 grows to substantially thesize of the inner diameter of the first fume tube 30 at the firsttapered region 30C.

Use of the example of the fume tube assembly 26 depicted in FIGS. 4A-Cmay be advantageous in providing a smooth, or gradual, transition forincreasing and/or decreasing the effective diameter of the aperture 38over the course of the silica soot laydown process. For example, duringthe early stage, the first and second tapered regions 30C, 34C of thefirst and second fume tubes 30, 34 may be coupled such that theeffective diameter of the aperture 38 is that of the inside diameter ofthe second fume tube 34. As the soot blank 58 of the optical fiberpreform 50 grows in size, the second fume tube 34 may be retracted intothe first fume tube 30 such that gas is allowed to pass through the gap148 and increase the effective diameter of the aperture 38. The smoothtransition of the second fume tube 34 into the first fume tube 30 mayallow for an even and homogenous increasing in the effective diameter ofthe aperture 38 as the soot blank 58 of the optical fiber preform 50grows in size. In other words, while the fume tube assembly 26 is in thedepicted configuration of FIG. 4A, the effective diameter of theaperture 38 may be small (i.e., the early stage) such that the firstspray size may be achieved and as the optical fiber preform 50 grows insize, the effective diameter of the aperture 38 may be proportionallyincreased until finally the second tapered region 34C is positionedrearward of the first tapered region 30C and the effective diameter ofthe aperture 38 is that of the first fume tube 30 to create the secondspray size (i.e., the late stage depicted in FIG. 4C). As the effectivediameter of the aperture 38, and thereby the spray size of the silicasoot, may be more closely tied to the present size of the soot blank 58,a greater capture efficiency may be achieved using the example depictedin FIGS. 4A-C.

Referring now to FIG. 5, a method 150 of operating the burner 10 isdisclosed. The method 150 may begin with step 154 of igniting a burnerhaving a fume tube assembly 26 to produce a first spray size of silicondioxide particles. As explained above, the first spray size of thesilica particles may be produced while the optical fiber preform 50 isin the early stage of formation. The ignition of the burner 10 maycorrespond to the ignition of the CH₄ and O₂ mixture, or to the burningof the OMCTS and O₂. Next, a step 158 of depositing the silicon dioxideparticles on the core cane 54 to produce the soot blank 58 is performed.The silica particles attach to the core cane 54 and slowly build up toform the soot blank 58. Next, a step 162 of adjusting the effectivediameter of the aperture 38 of the fume tube assembly 26 to produce thesecond spray size of the silicon dioxide particles may be performed. Asexplained above, the second spray size may be larger than the firstspray size. It will be understood that the step of adjusting theeffective diameter of the aperture 38 is performed while depositing thesilicon dioxide particles. In other words, the burner 10 may not need tobe turned off, or otherwise stopped, to adjust the effective diameter ofthe aperture 38. The adjustment of the effective diameter of theaperture 38 may be accomplished by moving the first and/or second fumetubes 30, 34 relative to one another.

The method 150 may further include a step of emitting gas proximate thefume tube assembly 26. As explained above, the gas may be emittedproximate the fume tube assembly 26 through any one of the gas emittingregions 22 (e.g., inner shield N₂, outershield O₂ and/or the CH₄ and O₂premix). The method 150 may further include a step of increasing a flowrate of the emitted gas after adjusting the effective diameter of theaperture 38. As the adjustment of the effective diameter of the aperture38 allows a greater amount of Siltet and/or OMCTS and O₂ to be emittedfrom the fume tube assembly 26, a corresponding increase in the amountof gas emitted from the emitting regions 22 may be increased to decreaseturbulence and homogenize the spray of silica particles. The method 150may further include a step of decoupling a tapered region (e.g., thesecond tapered region 34C) of the second fume tube 34 with a taperedregion (e.g., the first tapered region 30C) of the first fume tube 30.As explained above, decoupling of the first and second tapered regions30C, 34C increases the effective diameter of the aperture 38 and allowsa greater OMCTS and O₂ flow through the fume tube assembly 26. Themethod 150 may also include a step of moving the second fume tube 34 andthe third fume tube 140 within the first fume tube 30. As explainedabove, moving of the second and third fume tubes 34, 140 within thefirst fume tube 30 alters the effective diameter of the aperture 38 suchthat an increased OMCTS and O₂ flow may pass through the fume tubeassembly 26 without added turbulence.

Use of the present disclosure may offer a variety of advantages. First,altering of the effective diameter of the aperture 38 allow for theburner 10 to provide a variable spray size of silica particles. Thevariable nature of the spray size allows the burner 10 to provideincreased capture efficiency by producing a spray size that is based onthe current size and/or diameter of the soot blank 58 of the opticalfiber preform 50. Increase of the capture efficiency of the burner 10may aid in cost savings for the production of silica soot. Second, asthe effective diameter of the aperture 38 may be variably adjusted, alaydown rate, or rate of deposition of the silica soot on the opticalfiber preform 50 may be increased. Third, as the disclosed fume tubeassembly 26 is capable of adjusting the effective diameter of theaperture 38 dynamically while in operation, the burner 10 may not needto be shut down in order to increase laydown rate or change the spraysize of the silica soot particles.

Modifications of the disclosure will occur to those skilled in the artand to those who make or use the disclosure. Therefore, it is understoodthat the embodiments shown in the drawings and described above aremerely for illustrative purposes and not intended to limit the scope ofthe disclosure, which is defined by the following claims, as interpretedaccording to the principles of patent law, including the doctrine ofequivalents.

It will be understood by one having ordinary skill in the art thatconstruction of the described disclosure, and other components, is notlimited to any specific material. Other exemplary embodiments of thedisclosure disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms: couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature, or may be removableor releasable in nature, unless otherwise stated.

As used herein, the term “about” means that amounts, sizes,formulations, parameters, and other quantities and characteristics arenot and need not be exact, but may be approximate and/or larger orsmaller, as desired, reflecting tolerances, conversion factors, roundingoff, measurement error and the like, and other factors known to those ofskill in the art. When the term “about” is used in describing a value oran end-point of a range, the disclosure should be understood to includethe specific value or end-point referred to. Whether or not a numericalvalue or end-point of a range in the specification recites “about,” thenumerical value or end-point of a range is intended to include twoembodiments: one modified by “about,” and one not modified by “about.”It will be further understood that the endpoints of each of the rangesare significant both in relation to the other endpoint, andindependently of the other endpoint.

The terms “substantial,” “substantially,” and variations thereof as usedherein are intended to note that a described feature is equal orapproximately equal to a value or description. For example, a“substantially planar” surface is intended to denote a surface that isplanar or approximately planar. Moreover, “substantially” is intended todenote that two values are equal or approximately equal. In someembodiments, “substantially” may denote values within about 10% of eachother, such as within about 5% of each other, or within about 2% of eachother.

It is also important to note that the construction and arrangement ofthe elements of the disclosure, as shown in the exemplary embodiments,is illustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multipleparts, or elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures, and/or members, or connectors, orother elements of the system, may be varied, and the nature or numeralof adjustment positions provided between the elements may be varied. Itshould be noted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

It will be understood that any described processes, or steps withindescribed processes, may be combined with other disclosed processes orsteps to form structures within the scope of the present disclosure. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present disclosure, and, further, it is to beunderstood that such concepts are intended to be covered by thefollowing claims, unless these claims, by their language, expresslystate otherwise. Further, the claims, as set forth below, areincorporated into and constitute part of this Detailed Description.

What is claimed is:
 1. A method of forming an optical fiber preform,comprising the steps: igniting a burner having a fume tube assembly toproduce a first spray size of silicon dioxide particles; depositing thesilicon dioxide particles on a core cane to produce a soot blank; andadjusting an effective diameter of an aperture of the fume tube assemblyto produce a second spray size of the silicon dioxide particles, whereinthe second spray size is larger than the first spray size.
 2. The methodof claim 1, wherein the step of adjusting the effective diameter of theaperture is performed while depositing the silicon dioxide particles. 3.The method of claim 1, further comprising the step of: emitting a gasproximate the fume tube assembly.
 4. The method of claim 3, furthercomprising the step of: increasing a flow rate of the emitted gas afteradjusting the effective diameter of the aperture.
 5. The method of claim1, wherein the step of adjusting the effective diameter of the apertureof the fume tube assembly further comprises the step of: moving a secondfume tube within a first fume tube.
 6. The method of claim 5, whereinthe step of adjusting the effective diameter of the aperture of the fumetube assembly further comprises the step of: decoupling a tapered regionof the second tube with a tapered region of the first tube.
 7. Themethod of claim 1, wherein the step of adjusting the effective diameterof the aperture of the fume tube assembly further comprises the step of:moving a second fume tube and a third fume tube within a first fumetube.
 8. A burner, comprising: a back block; a face block defining aplurality of gas emitting regions; a fume tube assembly extendingthrough the face block and surrounded by the gas emitting regions,wherein the fume tube assembly comprises: a first fume tube coupled tothe face block; a second fume tube positioned within the first tube; andan aperture defined at an end of the fume tube assembly; and an actuatorcoupled with the second fume tube and configured to move the second fumetube within the first fume tube to adjust an effective diameter of theaperture.
 9. The burner of claim 8, wherein an exterior surface of thesecond fume tube is slidably coupled to an inner surface of the firstfume tube.
 10. The burner of claim 8, further comprising: a third fumetube slidably coupled with the second fume tube.
 11. The burner of claim10, wherein the actuator is further configured to move the third tuberelative to the second fume tube.
 12. The burner of claim 8, wherein anend of the second tube is positioned from about 2 mm to about 10 mminward from the aperture.
 13. The burner of claim 8, wherein an insidediameter of the first fume tube is from about 1 mm and about 4 mm. 14.The burner of claim 8, wherein an inside diameter of the second fumetube is from about 2.0 mm to about to 2.8 mm.
 15. A burner, comprising:a face block defining a plurality of gas emitting regions; a fume tubeassembly extending through the face block and surrounded by the gasemitting regions, wherein the fume tube assembly comprises: a first fumetube; a second fume tube movably positioned within the first tube anddefining an exterior surface, wherein the exterior surface is tapered;and an aperture defined at an end of the fume tube assembly; and anactuator coupled with the second fume tube and configured to move thesecond fume tube within the first fume tube to variably adjust aneffective diameter of the aperture.
 16. The burner of claim 15, whereina gap is defined between the second fume tube and the first fume tube.17. The burner of claim 15, wherein the actuator is further configuredto move the second tube through the aperture.
 18. The burner of claim15, wherein the actuator is configured to move the second fume tubecoaxial relative to the first fume tube.
 19. The burner of claim 15,wherein the first fume tube is tapered proximate the aperture.
 20. Theburner of claim 15, wherein an exterior diameter of second tube isapproximately equal to an inside diameter of the first fume tube.